[ColinDabritz]

The cue I learned for that was "the stick man is standing on the line | and leaning forward / or backward \ " (Which is of course western reading direction sensitive)

[tripzilch]

I always remembered it as, apparently they are both handwritten as an upwards stroke. Assuming western LTR reading direction, it means the slash forward goes forward, and the backslash goes backwards with respect to the reading direction.

I mean, I never really thought about it, but that's how I "know" which is slash forward and which is backslash.